EXCITATION OF QPESIC INSTABILITIES IN WEAKLY IONIZED PLASMAS PLACED IN NONPARALLEL FIELDS

Excitation of quasi-perpendicular electrostatic ion-cyclotron (QPESIC) instabilities in the vicinity of several lower-order harmonics of the ionic gyrofrequency is studied in a uniform and weakly ionized plasma placed in stationary and homogeneous non-parallel electric and magnetic fields. The pertaining threshold drifts are evaluated in both short- and longwave domains (i.e. for modal wavelengths respectively much smaller and much larger than the electron mean free path). It is assumed that the magnetization is sufficiently high to entail equal perpendicular drifts for both ions and electrons, cutting thereby off the perpendicular steady-state current. Nevertheless, the presence of the perpendicular drift is found to facilitate the excitation brought about by the steady-state current flowing along the magnetic lines of force. More precisely, the threshold drifts in both wavelength domains are shown to decrease as the angle between the fields is increased. The drifts also increase with T(e)/T(i) and with the order of the harmonic. Furthermore, the shortwave drifts are found to be sensitive to magnetization and to decrease generally as the magnetization increases.